The present invention relates to a cigarette manufacturing machine having an auxiliary tobacco feed unit.
Cigarette manufacturing machines are known to comprise an input chamber from which shredded tobacco is withdrawn by a carding unit and fed into a downflow duct. At the bottom end of the said downflow duct, provision is made for a conveyor for feeding the tobacco to the bottom end of an upflow output duct.
The said downflow duct usually acts as a store for a permanent column of tobacco, from the bottom end of which tobacco is withdrawn continually by a toothed roller and fed onto the said conveyor.
Known manufacturing machines of the aforementioned type are usually fed partly with recycled tobacco recovered downstream from the said upflow duct by means of shavers and usually fed directly into the said input chamber.
Owing to the small size of the recycled tobacco particles and, consequently, the difficulty with which they are withdrawn by the carding unit, such a solution does not always ensure a sufficiently even tobacco level inside the said downflow duct.
A major drawback resulting from this is an uneven stream of tobacco formed by the said toothed roller on the said conveyor and, consequently, uneven distribution of the tobacco inside the continuous cigarette rod formed at the output of the said upflow duct.
One known solution for overcoming this drawback is to feed the recycled tobacco directly into the downflow duct, and to arrange, over the width of the said duct, a number of level indicators for detecting the height of the said tobacco column at various points. The signals supplied by the said indicators provide for controlling supply of the recycled tobacco into the said downflow duct, so as to maintain a constant tobacco level over the entire width of the duct.
For this purpose, recycled tobacco is known to be fed into the said downflow duct by means of a substantially horizontal, swing tray designed to turn about an axis parallel with that of the downflow duct. See, for example, U.S. Pat. No. 4,524,781. The said tray presents an outlet smaller in width than the said duct, and shifts in response to the said signals for supplying recycled tobacco wherever it is needed for leveling off the top of the tobacco column.
As the said outlet moves through an arc of a circle, one drawback of the aforementioned swing tray is that it requires a downflow duct with a very large section, so large, in fact, that, due to the said duct acting as a tobacco store, the tobacco inside the duct tends to compact, thus resulting in uneven distribution on the said supply conveyor.
For leveling off the tobacco column inside the said downflow duct, another known auxiliary recycled tobacco feed unit provides for feeding the tobacco into the duct by means of a vibratory tray. The said tray is connected to one or more vibrating units designed to vibrate the tray by varying amounts at different points, depending on the signals supplied by the said tobacco level indicating means arranged at various points in the downflow duct. Consequently, instead of being constant over its entire width, the speed of the stream of tobacco fed onto the tray varies at different points, as required for leveling the tobacco column inside the downflow duct.
Auxililary feed units of the aforementioned type have only proved successful in compensating for relatively small, brief differences in the tobacco level inside the downflow duct. Futhermore, owing to the necessarily limited number of vibrating units employed and interaction between the same, such compensation is both inaccurate and slow in reponse to the control signals supplied by the said indicating means.